Belt guide and tensioning device for horizontal filters

ABSTRACT

Along the lower run of the endless carrier belts in a multiple belt horizontal filter, guides change the elevation of each belt relative to its adjacent belts; the clearance thereby produced between belts allows the mounting of lateral pressure means which push the belt edges to maintain the belts in proper alignment. A pressure-snubber assembly cooperates with the belt drive drum to reduce tension in the lower runs of the belts without causing belt slippage on the drive drum to consequently make the belts more responsive to edge alignment.

1 1 Oct. 2, 1973 United States Patent 11 1 Davis 210/401 X Kripski etal. 2l0/40l [5 BELT GUIDE AND TENSIONING DEVICE 3,314,545 4/1907 Grabbeet al...

FoR HORIZONTAL FILTERS 3,477,583 I1/ 1969 {75] Inventor: Steven S.Davis, Bountiful, Utah Primary Examiner samih N Zahama EnvirotechCorporation, Salt Lake Assislflm ExaminerT- Granger Cit UtahAttorney-Robert E. Krebs et al.

[73] Assignee:

[57] ABSTRACT the lower run of the endless carrier belts in a le belthorizontal filter, guides change the eleva- [22] Filed: Sept. 3, 1971Appl. No.: 177,628

Along multi P 52 US. Cl. 210/401 Ofeach relative to its i beltsftheclear- [511 Int Cl 33/14 ance thereby produced between belts allows the[58] Field at Search.................... 210/400, 401, 402; mounting oflateral Pressure means which p the bell es to maintain the belts inproper alignment. A pressnubber assembly cooperates with the belt drivedrum to reduce tension in the lower runs of the belts without causingbelt slippage on the drive drum to conedg sure- [56] References CitedUNITED STATES PATENTS sequently make the belts more responsive to edgealignment.

210/401 X 198/202 x v 2l0/40l X 7 Claims, 4 Drawing Figures Holland Y hD. f m 555 655 999 l// 620 PMENTEW'Z SHEET 1 [IF 2 INVENTOR. STEVEN S.DAVIS His Afforney PATENTEntm .zma 3'.1$2'.561

' SHEET 2 [IF 2 I4 I 53 F/G. 3 55 57 INVENTOR. STEVEN S. DAVIS BYFMZ/WHis Ahorney 1 BELT GUIDE AND TENSIONING DEVICE FOR HORIZONTAL FILTERSFIELD OF THE INVENTION This invention relates to continuous filtrationdevices in which an endless web of filter medium is supported andhorizontally carried on an endless carrier belt under a slurry so thatliquor from the slurry may be drawn down through the filter web, ontoand across the belt, and into suction means underlying the upper run ofthe belt. Generally the carrier belt is supported across such devices byrotatable drums at the opposite ends thereof, and one of the drums isthe drive. The filter web is usually separated from the belt adjacentone of the drums, and the filter cake is removed before the belt and webare rejoined to pass again over the suction means. Such devices may bereferred to as horizontal belt filters.

Wide filters may utilize two or more coplanar, reinforced-rubber,carrier belts. In some arrangements the belts are medially perforated sofiltrate drains therethrough; in other arrangements filtrate drainsthrough gaps left between adjacent belts. With either arrangement,drainage channels are usually formed by parallel grooves extendingtransversely of the belts. Regardless of the number of drainage belts,usually only a single filter web overlies the belts.

In any multiple belt filter, all belts must be maintained in properalignment with respect to each other and the filter, particularlythrough the filtration sequences on the upper run. Misalignment maydisrupt cake formation on the filter web or, where adrainage gap isutilized, disrupt the flow of filtrate. Although initially aligned, thebelts tend to bias across the drums with use. In some constructions alongitudinal rib is molded to the underside of the belt and the ribengages a track on the filter and/or on the end drums. Although such adesign willwork mechanically, there are'other shortcomings. The cost ofbelts'with such ribs is high, the added surface area of the rib sidesrubbing against the track increases friction, and the tracks must alwaysbe maintained in accurate alignment which increases the maintenancecost. I I

Variance in belt length is another problem in multiple belt filters. Thelongest belt must be tensioned to travel without slippage on the drivedrum. Since tension is created by stretching the belt between the enddrums, when the longest belt is properly tensioned, the shorter beltsmay be overstretched thereby causing early belt failure and making beltalignment more difficult. Moreover, thehigh tension on the shorter beltsmay overstress other components and may deform the drainage channels.

An object of the invention is to provide, in a horizontal belt filter,means to maintain frictional engagement between the belt and drive drumwith minimum tension on the belt;

another object is to provide, in a multiple belt horizontal filter,means to accommodate several belts-of different lengths while providingequal tension in all such belts during the filtration cycle whileavoiding excessive tension to any of the belts; and

another object is to provide means to effect corrective alignment of oneor more belts on a horizontal filter so that belts with smoothundersurfaces may be employed and maintained in proper alignment on thefilter.

BRIEF SUMMARY OF THE INVENTION In accordance with'the invention, guidingof the belts and the application of corrective aligning forces isaccomplished by means pushing against the belt edges as the belt passesthrough the lower run where it is free to move laterally. When multiplebelts are employed, the invention provides means for separating thelower runs of the several belts vertically from each other so thatspaces are provided for mounting the edge-engaging aligning devices.

Also, in accordance with the invention, by gripping the belt between'thedrive drum and a separate gripper roller, sufficient frictionalengagement is provided to enable the drive roll to pull the belt throughthe upper run while' permitting the belt to relax on the lower run. Thisrelaxation allows belt alignment correction to be achieved with onlylight lateral forces applied during the lower run. At the same time thegripper roller provides equal frictional forces between the drum and allthe belts even though the belts are of different lengths.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects and advantages of theinvention may be ascertained from the following description andaccompanying drawings, which are offered by way of example and not inlimitation of theinvention, the scope of the invention being defined bythe appended claims.

In the drawings:

FIG. 1 is a simplified viewv of a multiple belt filter em- DETAILEDDESCRIPTION OF THE INVENTION In the embodiment illustrated in FIGS. 1and 2, horizontally disposed drums l2 and 13 are rotatably mounted atopposite ends of a multiple belt horizontal filter to support at leasttwo endlesscarrier belts l4 and 15 in coplanar relationship horizontallyover a vacuum box 16 which is fixed .to the filter frame between thedrums. A conventional mechanism, not shown, drives the drum 13 in thedirection indicated by the curved arrow to move the carrier belts byfrictional engagement. An endless web of filter medium 17 overlies andis carried on the belts under a slurry poured from above the vacuum box.Also provided, but not shown, is y a vacuum source which connectsto thevacuum box to effect withdrawal of filtrate and air therefrom.

During their lower run, the elevations of the belts are changed so thatadjacent belts are at different elevations. Elongated guide rollers 21and 22, extending transversely of the belts, are rotatably mountedwithin the frame by any suitable means (not shown in detail) to 7 guidethe several belts to the various elevations. Then, rotatable spols 26and 27, guide shoes or the like, are suitably mounted from the frame(again by means not shown in detail) to be positioned adjacent the beltedges in the spaces between the belts thereby to laterallycorrectionally align each belt by pushing against its edges.

In FIG. 1, the relative elevation of the belts l4 and I5 is changed byraising upper belt a distance above a horizontal median plane of thelower run and lowering belt 14 approximately the same distance below themedian plane; the vertical displacement of both the belts from theirnatural course, when the belts are of equal length should be equal.Idler rollers 23 and 25 are rotatably supported on the frame to gentlypinch the belts against the respective associated guide rollers 21 and22. The idler rollers may be adjustable and are particularly useful withthinner belts or with belts having a tendency to warp.

An alternative arrangement, FIG. 4, involves raising one carrier belt 15by a guide roller 42 near the righthand drum [3 and then lowering thatbelt by a guide roller 43 near the left-hand drum 12; the other belt 14is lowered near the drum 13 by a roller 44 and is raised near the drum12 by a roller 45. Pairs of edge-engaging spools 47 may be provided tocorrectionally guide the belt before and after it leaves each of theguide rollers. This arrangement permits accommodation of a wider rangeof belt lengths and more lateral correction.

The efficiency of the above-described lateral guide systems is increasedwhen the tension in the lower run of the belts is decreased, and thepressure-snubber assembly of this invention is designed to permit filterop eration with low tension in the lower run of the belts. The tension(working tension) needed to pull the belts across thevacuum box is highbecause of the need to overcome drag across the vacuum box due to beltweight, slurry weight, and suctional force. It is known that the workingtension exerted by a belt around a drive drum is a function of thefrictional engagement between the drum and belt and,;'more particularly,is directly proportional to the tension existing on the other end-of thebelt (initial tension). In single belt arrangements, the driveand taildrums are simply pulled apart to stretch the belt to provide therequisiteinitial tension and the drums may be canted to provide beltalignment. In multiple belt systems, especially on long belts (I6-tofeet), the belt lengths'vary and, spreading the drive and tail drums totension, the longest belt may damage the shorter belts. Moreover, thetension extends'through the lower run of the belts thus subjectingtheentire belt to continuous tension as well as making belt alignmentmore difficult. Furthermore, when multiplebelts are utilized, beltalignment cannot be accomplished'bycanting of the drums. 1

v "Ihe present invention is predicated on; the discovery that, if thefrictional engagement between the. belt and drive drum is increased byforces applied solely at the drive drum,;the need for initial tension atthe opposite end "of the belt (that is, at the tail drum) is obviatedwith the result that the tensionih the lower run maybe relaxed. ThegripperrollerQof the pressure-snubber assembly of thislinventionaccomplishes that result. That is, the pressure-snubber assemblyprovides belt drive lected fixed angle. As illustrated, the spring 55urges the idler roller 51 against the belts near the bottom of the drum,thereby increasing the normal and frictional forces between the beltsand the drive drum 13 so that the belts may run upon the drum withoutslippage and with reduced tensions in their lower runs.

Belt working tension is also increased by increased wrap of the beltaround the drive drum. In FIG..1 the gripper roller 51 is so mountedthat it may be pivoted with respect to the drums axis to increase thebelt area in contact with the drum. The bearing block 53 is mounted onamarm 59 that is pivoted at its upper end and means such as a turnbuckleare provided adjacent the free end of the am to hold the arm in apre-selected position. As shown, the idler roll is spring tensioned toboth increase the normal force between the belt and drive drum and atthesame time to increase the wrap angle. In other respects, thatpressure-snubber assembly may be identical with the one shown in FIG. 3.The idler rollers 51 may be rubber covered to prevent damage to thedrainage channels formed across the carrier belts. I

Although the invention has been described with reference to simplifiedillustrations, it should be obvious that the various elements such asthe guide means ('exemplifiedby rollers 21 and 22) as well as theedgeengaging aligning means (exemplified as spools) may be suitablysupported in a variety of ways to provide for rotation and otheradjustment. Particularly,the latter may be resiliently mounted to beurged against the belt edges in a manner suchthat when the belt movestoward a spool, the resistance of that spool toward belt movementwillincrease whileon the edge guide on the opposite spool will unload oroffer a reduced resistance.

' '1. In-a multiple-belt horizontal filter having endless carrier beltsof substantially equal circumference trained around drums at oppositeends of the filter to provide a horizontal upper working run whereonsaid belts are substantially coplanar and a lower return run of the armmay be fixed to a frame member at a sedrive drum, the improvementcomprising:

a. guide means supported on the filter frame to engage the lower run' ofthe beltstosubstantially change the elevation of each belt in saidlowerrun relative to its adjacent belts; b. said guide means comprising:

l a plurality of rotatableguide rollers mountedfon I said frametransversely of sa id belts, at least" one of said guide rollers beingina differenthorizontal'plane relative .toanother one of saidrollers, andt 2. elongated idler rollers rotatably mounted on the filter to" pinchthe belts against corresponding ones of said guide rollers to retainsaid'belts flat;

c. lateral pressure means mounted on the filter and located in theclearance provided by the changed elevations of said belts and arrangedto act against the edges of said belts to correctively maintain saidbelts in parallel alignment by lateral inward pressure on said edges.

2. The improvement according to claim- 1 wherein saidguide meanscomprises at least one elongated guide roller mounted transversely ofthe belts outside the natural course of the lower run of said belts andalternate ones of said belts are trained to pass in engagement with saidroller.

3. An improvement according to claim 1 wherein said lateral pressuremeans comprises rotatable spools each of which is resiliently mounted onsaid frame adjacent the edge of a belt in said lower run and isrotatable about an axis substantially normal to the surface of said beltthereby to act against the edges of the belts to maintain beltalignment.

4. An improvement according to claim 1 wherein a first set of said guidemeans raise alternate ones of said belts to an elevation above ahorizontal plane near one end of the filter and lower the same belts toan elevation below the plane near the other end of the filter, and asecond set of said guide means, conversely, lowers and raises eachintermediate belt.

5. The improvement according to claim 1 with the addition of apressure-snubber assembly comprising a gripper roller rotatably mountedon the filter transverse of the belts and in contact therewith to presssaid belts against the drive drum to lessen tension in the lower runs ofthe belts without belt slippage on the drive drum.

6. The improvement according to claim 5 wherein said pressure-snubberassembly further includes urging means adjustably urging said gripperroller towards the drive drum.

7. The improvement according to claim 5 in which said gripper roller ismounted to pivot adjustably with respect to the axis of the drive drumthereby to selectively vary the wrap of the belts about the drive drum.

1. In a multiple-belt horizontal filter having endless carrier belts ofsubstantially equal circumference trained around drums at opposite endsof the filter to provide a horizontal upper working run whereon saidbelts are substantially coplanar and a lower return run for the belts,the drum at one end of the filter being a drive drum, the improvementcomprising: a. guide means supported on the filter frame to engage thelower run of the belts to substantially change the elevation of eachbelt in said lower run relative to its adjacent belts; b. said guidemeans comprising:
 1. a plurality of rotatable guide rollers mounted onsaid frame transversely of said belts, at least one of said guiderollers being in a different horizontal plane relative to another one ofsaid rollers, and
 2. elongated idler rollers rotatably mounted on thefilter to pinch the belts against corresponding ones of said guiderollers to retain said belts flat; c. lateral pressure means mounted onthe filter and located in the clearance provided by the changedelevations of said belts and arranged to act against the edges of saidbelts to correctively maintain said belts in parallel alignment bylateral inward pressure on said edges.
 2. The improvement according toclaim 1 wherein said guide means comprises at least one elongated guideroller mounted transversely of the belts outside the natural course ofthe lower run of said belts and alternate ones of said belts are trainedto pass in engagement with said roller.
 2. elongated idler rollersrotatably mounted on the filter to pinch the belts against correspondingones of said guide rollers to retain said belts flat; c. lateralpressure means mounted on the filter and located in the clearanceprovided by the changed elevations of said belts and arranged to actagainst the edges of said belts to correctively maintain said belts inparallel alignment by lateral inward pressure on said edges.
 3. Animprovement according to claim 1 wherein said lateral pressure meanscomprises rotatable spools each of which is resiliently mounted on saidframe adjacent the edge of a belt in said lower run and is rotatableabout an axis substantially normal to the surface of said belt therebyto act against the edges of the belts to maintain belt alignment.
 4. Animprovement according to claim 1 wherein a first set of said guide meansraise alternate ones of said belts to an elevation above a horizontalplane near one end of the filter and lower the same belts to anelevation below the plane near the other end of the filter, and a secondset of said guide means, conversely, lowers and raises each intermediatebelt.
 5. The improvement according to claim 1 with the addition of apressure-snubber assembly comprising a gripper roller rotatably mountedon the filter transverse of the belts and in contact therewith to presssaid belts against the drive drum to lessen tension in the lower runs ofthe belts without belt slippage on the drive drum.
 6. The improvementaccording to claim 5 wherein said pressure-snubber assembly furtherincludes urging means adjustably urging said gripper roller towards thedrive drum.
 7. The improvement according to claim 5 in which saidgripper roller is mounted to pivot adjustably with respect to the axisof the drive drum thereby to selectively vary the wrap of the beltsaboUt the drive drum.